1. Field of the Invention
The present invention relates to an update technology of map data stored in a car navigation system mounted on a mobile object such as a vehicle.
2. Description of the Related Art
In a car navigation system which performs a navigation using map data stored therein, it is necessary to update the map data according to the change of a map environment such as a new road being built or a new establishment being constructed. The newest map data is provided in some cases by either the newest map data itself or incremental update data between old map data and the newest one.
Because the incremental update data is composed of a difference between old map data and the newest one, it is smaller in many cases than the newest map data itself in a data size. However, because a car navigation system having received the incremental update data is required to perform a process of making the newest map data from the incremental update data and the old map data, it takes in some cases a long time and high processing load in updating the map data.
Consequently, according to Japanese Patent Laid-Open Publication No. 2006-251768, map data is composed of a plurality of files, and a ratio of a data size of a difference file to that of an updated file is calculated for every file; when the ratio is less than a predetermined ratio (for example, less than 10%), the difference file is provided; and when the ratio is not less than the predetermined ratio, the updated file is provided as it is.
In the meantime, when a data amount of map data to be updated is large, even if not incremental update data but updated map data itself is provided, it takes in some cases several ten minutes in updating. Furthermore, when a car navigation system updates the map data, in some cases the system stops all functions of using the map data until updating all map data is completed.
However, with respect to the map data, a data kind of data used is different in some cases according to a function: such as data used in a route calculate function; data used in a map drawing function; and data used in an address search function. Therefore, it is convenient for a user if a function that he/she wants to use is updated in order, and if the function using data in order from the data of a data kind whose updating is completed can be activated
Consequently, there is a need for updating map data in a car navigation system in order from a data kind of data designated by a user.